1. Field of the Invention
The invention relates to a high heat-resistance resin composition and a high heat-resistance insulated cable which uses the same.
2. Description of the Related Art
A conventional insulating material consisting of polyvinyl chloride (PVC) is generally used for an insulated cable. The insulating material which consists of PVC has good quality in characteristics for practical use and in price. However, a problem such as environmental contamination caused by waste disposal of the insulating material which produces gas containing chlorine or the like occurs, when the insulating material consisting of PVC is incinerates.
Further, the realization of light weight and thin thickness of an insulated cable is required in accordance with the request of light weight of a car body and the saving of a space for wiring cables in saving energy consumption in the area of transportation such as an automobile, a train or the like. In such a request of light weight and thin thickness of the insulated cable, however, there is a disadvantage in which such required characteristics as heat resistance and abrasion resistance are not realized, and so on, where the conventional PVC material is used for an insulated cable.
For these reasons, insulated materials other than PVC are required.
For responding to the requirement, in recent years, a polyester resin which is crystalline polymer is used for an insulating material. The polyester resin is used in the wide areas of an automobile, an electrical and electronic engineering, an insulating material, and OA (office automation) for the reason that the polyester resin has good quality in heat resistance, abrasion resistance, electrical property, chemical resistance leading to formability, and low water-absorbing property, and dimensional stability. This insulating material is described, for example, in the Japanese Patent No. 3650474.
A thickness of an insulation of an insulated cable for an automobile is conventionally 0.5 mm, and a thickness of the insulation of the cable is required to be thinner than a thickness of the conventional insulation by the formation of spreading an insulating material for the insulation of the cable.
There is a prospect for responding to such a request while keeping heat resistance and abrasion resistance, because a general-purpose engineering plastic represented by polyester resin has especially good quality in formability.
However, the polyester resin is a crystalline polymer, and has characteristics that heat absorption amount increases after thermal treatment, thus crystallinity degree of the crystalline polymer increases. For this reason, if the polyester resin is used for an insulating material which is spread to be formed for an insulation of an insulated cable, it is considered that a degree of extensibility of the crystalline polymer decreases. Therefor, a relation between the crystallinity degree of the crystalline polymer and the degree of extensibility thereof is important.
In addition, heat absorption amount at a melting point of a crystalline polymer that indicates a development of crystallinity of the crystalline polymer that causes a decrease of the degree of extensibility thereof, for example, is studied in some publications. Among these publications, however, bending property of the crystalline polymer and heat-sagging property that indicates a sag of a sample after thermal treatment are only studied as described in the Japanese Patent Kokai No. 2006-232977, and a recrystallization-beginning temperature of the crystalline polymer is only studied as described in the Japanese Patent Kokai No. 2004-264803, while the relation between the crystallinity degree of the crystalline polymer and the degree of extensibility thereof is not studied therein.
In order to suppress the increase of a heat absorption amount of the crystalline polymer, that is the development of a crystallinity degree of the crystalline polymer, there is a conventional technique in which monomer having bending property is added to a material of the polyester resin as described in the Japanese Patent Kokai No. 2005-213441, but the relation between the crystallinity degree of the crystalline polymer and the degree of extensibility thereof is not studied even in this publication.
As described in the above publications, although the polyester resin has good quality in formability or the like, the polyester resin is a crystalline polymer so that the crystallinity degree of the polyester resin is progressed by thermal treatment and the heat absorption amount at the melting point of the polyester resin is increased and the degree of extensibility thereof is resultantly decreased to a large extent. In addition, if the polyester resin is applied to an insulated cable, spreading formation of an insulating material which is an outer insulating layer of the insulated cable is disturbed, and the request of thin thickness of the insulating material is not realized.